Leptohalysis kaikoi, Kitazato, Uematsui, Todo & Gooday, 2009

Kitazato, Hiroshi, Uematsui, Katsuyuki, Todo, Yuko & Gooday, Andrew J., 2009, New species of Leptohalysis (Rhizaria, Foraminifera) from an extreme hadal site in the western Pacific Ocean, Zootaxa 2059 (1), pp. 23-32 : 24-28

Leptohalysis kaikoi sp. nov.

Figs 1–2

Leptohalysis sp. 3 . Todo 2003, pl. 14, fig. 7

Leptohalysis sp. Todo et al. 2005

Diagnosis: Species assigned Leptohalysis with minute test (<130 µm long, ~20 µm wide), comprising more or less linear series of chambers, increasing slightly but regularly in size to give elongate, gently tapered form. Chambers globular, abutting with only slight overlap. Wall finely agglutinated, mainly comprising grains with flat exposed faces that abut to create outer surface resembling uneven pavement; edges of grains obscured by copious amounts of organic cement.

Type Locality: The Challenger Deep (11º 20.093’ N, 142º 11.803’ E; depth of 10,896 m), Mariana Trench, Pacific Ocean

Type specimens: The type specimens are deposited in the National Science Museum , Tokyo under registration numbers MPC-02690 (holotype) and MPC-02691-02696 (6 paratypes) .

Other material examined. 16 specimens

Ethmology From Kaiko (Japanese) = trench and also the name of the ROV used to collected the material from the Challenger Deep.

Description. Test morphology. Test reddish-brown in colour, although colour intensity varies considerably between specimens and later chambers often paler than earlier ones. In one paratype ( Fig. 1C ),

first 8 chambers have dark, ferruginous appearance and contrast strikingly with final 3 very lightly-coloured chambers. Test comprises linear series of 7–12 (usually 10–11) chambers following more or less straight, gently curved to slightly sinuous course. Overall test length 80–127 µm (mean 110.1 ± 13.7 µm); length:width ratio 4.6–6.0 (mean 5.5 ± 0.34). Proloculus forms small, basically organic sphere, 6–10 µm diameter. All subsequent chambers agglutinated, approximately spherical and pressed against each other to create segmented appearance. Width of smallest (proximal) chamber 6–9 µm (mean 8.1 ± 1.1 µm) and largest (distal) chamber 16–21 µm (mean 19.8 ± 1.63 µm). Tiny additional semicircular or dome-like chamber (3–5 µm diameter) sometimes positioned to one side of main test axis, between proloculus and adjoining chamber. Aperture simple, more or less circular opening at end of final chamber.

Wall structure and composition. Wall comprises tiny agglutinated particles, typically 2–4 µm in size. Individual chambers formed from grains of different sizes; for example, 1.3–3.0 µm and 1.8–2.8 µm in chambers illustrated in Fig. 2 . Final two chambers incorporate larger grains (5–10 µm diameter). Edges of particles usually covered by cement, obscuring their precise shapes. However, most appear approximately equidimensional and subangular in outline. Many particles have flat exposed surfaces, sometimes with traces of flake-like cleavages. Some better exposed grains are thin and plate-like; others appear more rounded. X-ray microanalysis suggests that grains are composed mainly of Si and Al with traces of Mg, Mn, K and sometimes Fe, consistent with clay mineral composition.

Grains fringed by copious amounts of cement which overlap to varying extent onto their flat surfaces. Isolated spots of cement also present in some areas. Cement forms tightly-meshed, spongy mass consisting partly of anastomosing, bar-like elements. Small, flat areas within cement mass are probably tiny clay particles.

Proloculus transparent with very smooth surface, composed mainly of organic material, with scattering of tiny grains, some rod shaped, in some areas. X-ray microanalyses reveal peaks for Si and Al as well as Mg, Ca and Fe, presumably derived from these grains.

Remarks. The description of the wall structure is based mainly on the specimen examined by SEM and illustrated in Fig. 2 . Three other specimens examined by SEM had a similar wall structure, but because of long immersion in glycerol they were not sufficiently well preserved to be illustrated.

Leptohalysis (type species Reophax catella Höglund 1947 ) was originally diagnosed as follows: ‘A genus of the Hormosinidae characterised by an elongate delicate test composed of slowly enlarging, distally tapering, flask-shaped chambers with blunt bases’ ( Loeblich & Tappan 1984). It was distinguished from Reophax based on ‘the very elongate and delicate test, slowly enlarging flask-like chambers in nearly straight series, and flexible wall with distinct organic component and sparse agglutinated material in the early stage’ ( Loeblich & Tappan 1984). The new species conforms to this description in several respects. However, it differs from typical representatives of the genus in the following respects. 1) The shape of the chambers, which are rounded and abut closely with a distinct suture between them rather than being flask-shaped with more or less flat, truncated bases. 2) The relatively thick wall that consists mainly of grains with flat exposed faces that abut to create a surface resembling an uneven pavement. The edges of the particles are obscured by copious amounts of organic cement rather than being delicately constructed from flake-like, slightly overlapping grains. 3) The presence of a single "adventitious" chamber following the proloculus and located to one side of the axis of growth. Leptohalysis kaikoi also resembles Scherochorella Loeblich and Tappan 1984 , a hormosinid genus based on a Lower Carboniferous type species but including one Holocene species, Reophax barwonensis Collins 1974 ( Loeblich & Tappan 1984). The main features that distinguish the new species from Scherochorella are as follows: 1) the chambers are globular in shape and much more distinctly separated, 2) the proloculus is transparent and spherical rather than bulbous and 3) the test is much smaller, <130 µm compared to 570 µm in R. barwonensis ( Collins 1974) .The only hormosinacean genus of comparable size is Siliconodosarina Colom 1964 from the Ria de Vigo in NW Spain, which measures only 90 µm in length. It is distinguished from L. kaikoi by the shape of the chambers, the serrated margin, the thicker agglutinated wall and the agglutinated proloculus ( Loeblich &Tappan 1987).

For the present, we adopt a conservative approach and place the new species in Leptohalysis , a genus that is widely distributed in the deep sea. A detailed comparison of its wall structure with that of typical representatives of Leptohalysis may provide the basis for establishing a new genus.

Figures

FIGURE 1: Leptohalysis kaikoi sp. nov., photographs taken using transmitted light. A: Holotype, reg. no. MPC-02690. B–G: Paratypes, reg. nos MPC-02691-02696. H–P: Additional unregistered specimens. Scale bars = 50 µm.

FIGURE 2: Leptohalysis kaikoi sp. nov., scanning electron micrographs. A: Complete specimen. B; Proximal end showing organic-walled proloculus. C: Central part of test showing grains with flat exposed surfaces. D: Aperture. E: Patches of organic cement on grain surfaces. F–G: Outer surface showing agglutinated grains embedded in copious amounts of organic cement.